A hard disk drive comprises one or more platters or disks that are coated with material that is magnetizable. Physical locations on the disk are associated with memory locations or memory addresses. Each location may represent a single bit of information: a logic high or a logic low, depending on the polarity of the magnetization. The data stored on the disk may be read by a sensor, for example a magnetoresistive sensor, that is able to detect the magnetic polarity transitions at memory locations on the disk as the disk rotates. Memory locations are typically distributed on the disks in circular lanes called tracks. Because memory locations may be distributed across the disk with a uniform density per unit area, more memory locations may be read per unit of time in tracks near the outer circumference of the disk than in tracks near the center of the disk. The sensors may be referred to as read heads and may comprise read sensors as well as other components. The output of the sensors, which may be referred to as readback data, may have very low signal strength. A preamplifier may be located relatively close to the sensors to significantly boost the sensor output before driving the boosted readback data to a circuit board or system on a chip (SoC) in a hard disk drive enclosure. The hard disk drive may comprise a write head to write data to the disk and a sensor to determine a distance of the read head and/or the write head from the surface of the disk. The hard disk drive may monitor and adjust the height of the read head and/or the write head above the disk, typically to maintain a preferred height.
Optical disk drives may share some commonalities with hard disk drives. The memory locations in an optical disk drive are read by directing a laser beam onto the memory location and reading back reflection of the laser beam by a photodiode, for example. If a pit in the surface of the disk is present at a memory location, the reflected light adds out-of-phase with other laser reflected light, adding destructively, and the photodiode detects less light. If no pit in the surface of the disk is present at the memory location, the reflected light adds in-phase, and the photodiode detects relatively more light. The output of the photodiode (e.g., readback data) may be amplified by a preamplifier before driving the readback data to the circuit board or SoC of the optical disk drive.